Control of Blood Vessel Function

Question 1

what do blood vessels contain in their walls that allows control of their radius

Answer 1

smooth muscle

active tension controls the radius of vessel

Question 2

what is the chief resistance vessels of systemic circulation

Answer 2

arterioles

Question 3

what regulates Q

Answer 3

local arteriolar resistance regulates Q to the tissue downstream of arteriole

the range of Q can be large

Question 4

what is flow matched to

Answer 4

metabolic requirements

ex. tissue or organ that works harder will need more flow

Question 5

what is basal tone

Answer 5

arterioles (and some larger vessels) have a natural degree of tone in their vascular smooth muscle

even if sympathetic innervation is removed there is some constriction

important if vessels are to be dilated

tissues with highest increased in Q (ex. skeletal muscle, salivary glands) have highest basal tone

Question 6

what influences basal tone

Answer 6

1. local factors: located in tissue (ex. tissue metabolites)
2. extrinsic factors: autonomic control

which type is dominant type of control depends on tissue

Question 7

what factors dominate in critical tissues

Answer 7

local control dominates

must have enough blood to meet metabolic needs on a second to second basis in order for the animal to survive (heart, brain, skeletal muscle)

Question 8

where does extrinsic control dominate

Answer 8

extrinsic control dominates in tissues that can withstand a temporary decrease in Q (kidney, splanchnic, resting skeletal muscle)

Question 9

where is an example where both local and extrinsic control are important

Answer 9

skin

Question 10

what are the local control mechanisms that influence basal tone

Answer 10

1. temperature
2. compression
3. myogenic response
4. local metabolites
5. autocoids

Question 11

how does temperature influence basal tone

Answer 11

important in skin

heat the cutaneous arteriole and veins and the dilate (ex. reddening of skin in hot water)

cool them and they constrict

direct effect of temperature on vascular smooth muscle cells

Question 12

what is paradoxical vasodilation

Answer 12

cool below 12 degrees and you get paradoxical vasodilation due to inhibition of neurotransmitter release –> reddeing of face in cold weather

Question 13

how does compression influence basal tone

Answer 13

stops Q

ex. squeeze skin

can lead to ischemia and infarction

Question 14

what are physiological examples of mechanical compression

Answer 14

1. coronary Q: heart twists to push blood out of aorta –> occludes vessels –> when it relaxes it opens the vessels up and thats when heart gets oxygen supply (if diastolic period reduced too much the heart blood supply will be reduced)
2. skeletal muscle contraction: will pump blood back up towards the heart

Question 15

how does myogenic response influence basal tone

Answer 15

transmural –> high external pressure will compress BV and impair Q

raising internal pressure distends BV but most arterioles (and some arteries) react by contracting –> myogenic response

intrinsic property of the vascular smooth muscle cell

Question 16

how do local metabolites influence basal tone

Answer 16

most important mechanism regulating vascular smooth muscle

many by-products of normal tissue metabolism cause vascular relaxation –> any increase in metabolic rate of a tissue causes arteriolar dilation and increases local tissue perfusion

metabolic vasodilation or metabolic hyperemia

Question 17

what are examples of local metabolites

Answer 17

active factors may be acidosis (due to CO2 and lactic acid)

ATP breakdown (ADP, AMP)

K+ released by muscle –> mechanism of factors are varied and can be complex

Question 18

how do autocoids influence basal tone

Answer 18

vasoactive chemicals produced locally, released locally and acting locally –> histamine, bradykinin, 5-hydroxytryptamine, prostaglandin, thromboxane-leukotriene group, nitrous oxide

all involved in special local responses such as inflammation and hemostasis

some cause vasodilation (bradykinin, PGE) some cause vasoconstriction (5HT, PGF)

some mixed histamine dilates arterioles, constricts veins

Question 19

what are extrinsic control of peripheral Q

Answer 19

CNS imposes control system over circulation

Question 20

what are afferent inputs for peripheral Q

Answer 20

sensory input –> baroreceptors

Question 21

what are efferent controls of peripheral Q

Answer 21

ach symp: vasodilator fibres

NA symp: vasoconstrictor fibres

parasympathetic vasodilator

heart: symp and parasymp

adrenal medulla: symp

Question 22

how do extrinsic and local factors work together

Answer 22

extrinsic predominates over “non-critical” organs (kidney, splanchnic) and controls HR and cardiac contractility

local factors regulate critical organs

so extrinsic mechanisms may increase HR and contractility this increases metabolic rate which then triggers local control mechanisms to dilate (ex. coronary arteriole and so increase coronary Q)

Question 23

how do hormones control circulation

Answer 23

1. several endocrine secretions have acute effects on heart and circulation
2. normally however these are less important than neural mechanisms for short-term control of CVS
3. if neural control is impaired (ex. heart transplant) or in pathological conditions (ex. hemorrhage) the endocrine secretions are important

Question 24

what are the effects of adrenaline

Answer 24

adrenal medulla secretes adrenaline and NA in response to sympathetic stimulation

adrenaline is major component

secretions made in fight or flight, exercise, hypotension, hypoglycemia

Question 25

what are baroreceptors and where are they found

Answer 25

sense changes in pressure

BR and non-encapsulated nerve endings in arteries at aortic arch and carotid sinus

Question 26

what cranial nerve responds to changes in pressure from the carotid sinus

Answer 26

afferent fibres from the carotid sinus ascend in the IXth cranial nerve glossopharyngeal

Question 27

what cranial nerve responds to changes in the aorta

Answer 27

aortic BR ascend in the X vagus nerve

Question 28

what are the goals of baroreceptors

Answer 28

aimed at stabilized blood pressure

Question 29

what do BR respond to

Answer 29

are mechanoreceptors responding to stretch

increased pressure in artery causes distention and this excites the receptors

Question 30

what are the responses to decreased pressure

Answer 30

1. increase sympathetic activity: increased HR, increased contractility
2. decreased parasympathetic activity: increased HR

both 1 & 2 increase CO

3. increased sympathetic activity: arteriole vasoconstriction (esp. kidney, splanchnic, resting skeletal muscle, non-critical organs)

leads to increase in TPR –> rediverts blood to essential organs but maintain a resistance

CO x TPR = blood pressure

increase of adrenaline from adrenal stimulates the heart

Question 31

what are the response to decreased pressure

Answer 31

BR reflex help to compensate for increased or decreased blood pressure (not cure it)

reflex is rapid and powerful (ex. hemorrhage which would decrease BP)

BR reflex also maintains pressure during changes in posture or activity

Question 32

what is BR adaptation

Answer 32

while BR can regulate moment to moment changes in BP they cannot regulate BP in long term

BR adapts (or are reset) to the prevailing level of arterial pressure (either up or down)

so in animals which are hypertensive over the long term the BR come to accept this as normal and regulate pressure at the elavated level

this resetting can be centrally mediated (ex. exercise the reflex is reset centrally) it can also be mediated peripherally –> happens if high BP is maintained

Question 33

what are the additional effects of the BR

Answer 33

1. sensation of thirst
2. increasing ADH which decreases urine flow from kidneys
3. increases renin which acts to produce aldosterone which decreases Na excretion (conserves water and maintains BP)